Rapid propidium monoazide cPCR assay for exclusive quantification of viable Salmonella spp. cells

Combination of pretreatment with propidium monoazide by competitive polymerase chain reaction (cPCR) was evaluated to enumerate the viability of Salmonella spp. The results showed that PMA treatment was effective in preventing the cPCR detection of target sequences from non-viable cells. In less than 5 hrs, this method generated a signal from viable but nonculturable (VBNC) Salmonella spp. The standard culture method gave approximately 1-2 log10 cfu ml-1 less as compared to the PMA-cPCR results. These results provided evidence to support the VBNC state, whereas, the viable cells failed to be cultured by SCM. The proposed method did not detect DNA from dead Salmonella spp. but recognizes the infectious potential of the VBNC state and is thereby, able to assess the effect of control strategies and provide trustworthy data for risk assessment.